This invention relates generally to inflatable passive restraint systems for use in vehicles for restraining the movement of a seated occupant such as in the event of a collision and, more particularly, to improved assemblies for providing an inflation fluid to an associated inflatable vehicle occupant restraint.
It is well known to protect a vehicle occupant by means of safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., "passive restraint systems." Such systems commonly contain or include an inflatable vehicle occupant restraint, such as in the form of a cushion or bag, commonly referred to as an "airbag cushion." In practice, airbag cushions are normally housed in an uninflated and folded condition to reduce or minimize space requirements. Typically, upon actuation of the system, such as when the vehicle encounters a sudden deceleration as in the event of a collision, the associated airbag cushion is designed to inflate or expand in a matter of no more than a few milliseconds.
Airbag cushion inflation or expansion is generally effected via an inflation fluid, e.g., a gas, produced or supplied by a device commonly referred to as an "inflator." An airbag cushion is desirably deployed into a location within the vehicle between the occupant and certain parts of the vehicle interior, such as a door, steering wheel, instrument panel or the like, to prevent or avoid the occupant from forcibly striking such part(s) of the vehicle interior.
Various types or forms of passive restraint assemblies have been developed or tailored to provide desired vehicle occupant protection based on either or both the position or placement of the occupant within the vehicle and the direction or nature of the vehicle collision. For example, driver side and passenger side inflatable restraint installations have found wide usage for providing protection to drivers and front seat passengers, respectively, in the event of head-on types of collisions while side impact inflatable restraint installations are typically more directed to vehicle occupant protection in the event of various vehicular impacts inflicted or imposed from directions other than head-on.
Many types of inflator devices have been disclosed in the art for the inflation of airbag inflatable restraints. One type of known inflator device derives inflation gas from a combustible pyrotechnic gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the airbag. Other common or known types of inflator devices include compressed stored gas inflators and hybrid inflators (e.g., inflators which utilize or rely on a combination of stored compressed gas and combustion of a gas generating material, e.g., a pyrotechnic, to produce or form an inflation gas for an associated airbag cushion).
In view of possibly varying operating conditions and, in turn, possibly varying desired performance characteristics, there is a need and a desire to provide what has been termed a "multistage" or "adaptive" inflation assembly and a corresponding inflatable restraint system. With an adaptive inflation assembly, output parameters such as the quantity, supply, and rate of supply of inflation fluid, for example, can be selectively and appropriately varied dependent on one or more selected operating conditions such as ambient temperature, occupant presence, seat belt usage and rate of deceleration of the motor vehicle, for example.
Various proposed or currently available dual stage inflation assemblies appear based on the principle of packaging together two separate inflator devices. While adaptive assemblies and systems are generally desirable for various applications, such dual stage inflation assemblies typically require the inclusion of additional components as a part of the associated inflator devices, thus undesirably increasing one or more of the size, cost and weight of the inflation assembly. For example, such inflator device combinations commonly include two distinct pressure vessels, two sets of filter or inflation gas treatment components, one for the output of each of the pressure vessels, and two distinct diffusers, again one for the output of each of the pressure vessels. Thus, the providing of an adaptive inflation assembly which will satisfactorily meet the size, cost and weight limitations associated with modern vehicle design, particularly as it pertains to driver side applications, has been difficult.
Those skilled in the art will appreciate that the rate at which gas is produced via the combustion of pyrotechnic materials is generally dependent upon the specific characteristics such as burn rate, density, geometry, combustion pressure and gas conversion percentage associated with the particular pyrotechnic material. In general, due to the commonly large pressure dependency of the burn rate of such pyrotechnic materials, it is preferred or necessary that the pressure within a respective inflator housing be maintained within certain limits in order to achieve optimum combustion operation. Unfortunately, various known multistage inflator designs include a single set of throttling orifices for the control of the pressure associated with the multiple pyrotechnic charges contained therewithin. As a result, such multistage inflation designs are not conducive to design optimization. In particular, multistage inflation assemblies must generally be capable of operating in various manners, dependent on the specifics of the incident or event leading to the actuation thereof. As such incident or event specifics are not known at the time of system design or installation, the exit orifices for such multistage inflation designs are typically not sized for optimum combustion but rather to provide an adequate margin of safety when all charges are deployed simultaneously. Pyrotechnics which are burned at less burned at less than optimum pressure are prone to producing increased proportions of various undesirable species such as carbon monoxide and oxide of nitrogen.
Further, inflatable restraint system designs are typically tailored to correspond to the specific vehicle design in which the system is to be installed. A key variable in the specific design of such systems often involves the specific fashion by which the inflatable restraint system is connected, joined or fastened within a particularly designed vehicle. As will be appreciated, such variability may undesirably complicate the manufacture and production of inflatable restraint systems for differently designed vehicles. For example, common inflatable restraint system designs may require complicated, costly, time-consuming or otherwise undesirable tooling, manufacturing or production changes in order to provide required design specificity for particular vehicle installations.
Thus, there is a need and a demand for an adaptive or multistage inflation assembly which more readily permits the independent throttling of the inflation medium discharged from each of the stages thereof. Further, there is a need and a demand for inflatable restraint system installations which more readily permit either or both design specificity and tailorability without necessitating undesirably complicated, costly or time-consuming tooling, manufacturing or production changes in order to provide required design specificity for particular vehicle installations. In particular, there remains a need and a demand for an adaptive inflation assembly, especially for driver side applications, of simple design and construction and such as may more readily satisfy installation size limitations and vehicle design specificity.